Total versus inhalable sampler comparison study for the determination of asphalt fume exposures within the road paving industry

Abstract

Exposure to asphalt fumes has a threshold limit value (TLV^®) of 0.5 mg m⁻³ (benzene extractable inhalable particulate) as recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). This reflects a recent change (2000) whereby two variables are different from the previous recommendation. First is a 10-fold reduction in quantity from 5 mg m⁻³ to 0.5 mg m⁻³. Secondly, the new TLV^® specifies the “inhalable” fraction as compared to what is presumed to be total particulate. To assess the impact of these changes, this study compares the differences between measurements of paving asphalt fume exposure in the field using an “inhalable” instrument versus the historically used ‘total’ sampler. Particle size is also examined to assist in the understanding of the aerodynamic collection differences as related to asphalt fumes and confounders. Results show that when exposures are limited to asphalt fumes, a 1 ∶ 1 relationship exists between samplers, showing no statistically significant differences in benzene soluble matter (BSM). This means that for the asphalt fume ACGIH TLV^®, the ‘total’ 37-mm sampler is an equivalent method to the “inhalable” method, referred to as IOM (Institute of Occupational Medicine), and should be acceptable for use against the TLV^®. However, the study found that when confounders (dust or old asphalt millings) are present in the workplace, there can be significant differences between the two samplers' reported exposure. The ratio of IOM/Total was 1.37 for milling asphalt sites, 1.41 for asphalt paving over granular base, and 1.02 for asphalt over asphalt pavements.